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Saturday, January 1, 2011

Deep time, geologic time, and the geologic time scale are intertwined concepts relating to the age of the earth, the long epochs, periods, eras, and eons of earth time, a time that is so long compared to our ordinary, everyday time, or even to historic time, that it took some number of years for it to be recognized. We in the west were formally introduced to geologic time by James Hutton, the father of geology. In Theory of Earth, published in 1788, he said:

For having, in the natural history of this earth, seen a succession of worlds, we may conclude that there is a system in nature; in like manner as, from seeing revolutions of the planets, it is concluded, that there is a system by which they are intended to continue those revolutions. But if the succession of worlds is established in the system of nature, it is in vain to look for anything higher in the origin of the earth. The result, therefore, of this physical enquiry is, that we find no vestige of a beginning,—no prospect of an end.

The Persian polymath, Avicenna, had come to a similar conclusion more than 700 years before Hutton:

Either they [mountains] are the effects of upheavals of the crust of the earth, such as might occur during a violent earthquake, or they are the effect of water, which, cutting itself a new route, has denuded the valleys, the strata being of different kinds, some soft, some hard... It would require a long period of time for all such changes to be accomplished, during which the mountains themselves might be somewhat diminished in size. [quoted by Toulmin and Goodfield, 1965]

John McPhee took us a little deeper in 1981, when he introduced the phrase "deep time" as a proxy for geologic time in his book Basin and Range. Prior to that, geologic time was the realm of geologists; since then, deep time has become a part of our everyday vocabulary. John McPhee, in essence, gave geologic time to non-geologists.

As a geologist, I've studied geologic time at least since high school, when I took Earth Science as an elective, extra science. I knew of geologic time prior to that, going back possibly into my early or middle childhood, when I became fascinated with rocks, minerals, volcanoes, trilobites, and dinosaurs, and when I probably learned some of the names of the geologic time periods and eras, such as Cretaceous. (Wikipedia shows the ages, epochs, periods, eras, eons, and supereons of the earth better than the geologic time scale linked to earlier; also see the ICS Geologic Time Scale). Did I understand the vast amount of time involved between trilobites and dinosaurs? I don't know.

I do know that thinking in terms of geologic time has become somewhat commonplace for me, and it seems to be primarily a matter of numbers and scale, and something that I visualize. My life fits inside a linear view, which runs from left to right in front of me: my birth being to the left, today being right in front of me, and my imagined latest years, even somewhat beyond likelihood, being to the right. When I think of history going back to the time change from B.C. to A.D., 1 A.D. is on the left, and everything else is relatively squished as it approaches today, which is still right in front of me. So, what about the 2 million years or so of Pleistocene glacial and interglacial intervals? Now, I've placed the beginning of the Pleistocene over to the left, our general time or the last century is right in front of me. At this point, I can't help but look farther left, beyond the beginning of the Pleistocene, where I can easily see the entire Tertiary back to 65 million years ago.

If I think of all of geologic time — the time frame during which the Earth existed, the last 4.6 billion years — things get even more squished on the end towards our current time, and I've often at this point managed to seat myself firmly in the early Paleozoic, Cambrian maybe, about 600 million years ago. The Precambrian is off to the left, and everything else off to the right. Sometimes I look at this sliding geologic time scale from the end of the Paleozoic, toward the Mesozoic, knowing (even though the Paleozoic rocks and fossils didn't know) that dinosaurs and the massive intrusions of the Sierra Nevada will be coming along as geologic time progresses.

And so, viewing all of geologic time, or particular parts of geologic time, requires me to slide my view to the right and left — or to slide time itself — while expanding or contracting the detail of the time frame, depending on what I want to look at. And when I'm reading about a particular time — whether historic, pre-historic, or geologic — the view often shifts until that the particular time is right in front of me, with time after that, including present time, over to the right.

Another thing I find myself doing when trying to view geologic time — and possibly this happens because I've read so many science fiction books set in countless future timelines — is to include future histories and future geologic time frames in my view, way off to the right. I do this when thinking about the future of the Earth, Solar System, and Universe, and also when thinking about things happening on Voyager in the 24th century (Star Trek timeline), or on the planet Path (Ender’s Universe). Often, this future time looks dark, with a lot of scattered stars and star systems. Or, once again, if I'm reading or watching books or movies set in these future timelines, that present is right in front of me, and our current present — their past — is to the left.

Some time ago, I read In Search of Deep Time by Henry Gee. Early in the book, he gets into a description of deep time, based in part on what John McPhee said in Basin and Range:

McPhee meant the term to refer to the immense intervals, measured in millions of years, disccussed as if they were days or weeks in the conversation of geologists: yet in reality, the intervals of geological time are too long to be readily comprehensible to minds used to thinking in terms of days, weeks and years--decades, at most.

He goes on, after showing a standard geological time chart:

But apart from telling you that Deep Time is long, conventional accounts never consider the implications of the scale of Deep Time on the way we think about evolution [I extrapolate, here, to include other geological occurrences and events]. If, as McPhee says, Deep Time implies intervals more or less incomprehensible to humans, we are entitled to ask whether it is valid to tell stories about evolution according to the conventions of narrative or drama. If it is not, then every story we tell in which causes are linked with effects, and ancestors are linked with descendants, becomes questionable: we can no longer use Deep Time as a backdrop for the stories we tell ourselves about evolution, and how and why we came to be who we are.

Once we realize that Deep Time can never support narratives of evolution, we are forced to accept that virtually everything we thought we knew about evolution is wrong. It is wrong because we want to think of the history of life as a story; but that is precisely what we cannot do. This tension--between Deep Time and the everyday scale of time--is the theme of this book. – Gee, In Search of Deep Time, Introduction

I didn't really find or feel much of that tension when reading his book, and was really looking forward to reading something deeper about deep time. The book, instead, is primarily about certain mechanical aspects of evolution (cladistics), which are really beyond me as a hard rocker, but which were nevertheless fascinating. I can't really comment as to their usefulness, but can refer you to this New York Times review of the book. As a geologist, I disagree that geologic time intervals are too immense to be comprehended. Perhaps it's a conceit for me to think so. Perhaps it's as McPhee says:

Geologists, dealing always with deep time, find that it seeps into their beings and affects them in various ways. ... In geologists' own lives, the least effect of time is that they think in two languages, function on two different scales. – McPhee, Basin and Range

Now, as an aside, I'd like to take deep time in literature farther back than John McPhee, to the "deeps of time" of J.R.R. Tokien.

Quotes from Tolkien on the deeps of time:
Out of the shadows the hobbits peeped, gazing back down the slope: little furtive figures that in the dim light looked like elf-children in the deeps of time peering out of the Wild Wood in wonder at their first Dawn. – The Two Towers, Book III, Chapter 3 [quoted here]

And She that walked in the darkness had heard the Elves cry that cry far back in the deeps of time, and she had not heeded it, and it did not daunt her now. – The Two Towers, Book IV, Chapter 9

As it drew near the great furnaces where, in the deeps of time, it had been shaped and forged, the Ring's power grew, and it became more fell, untamable save by some mighty will. – The Return of the King, Book VI, Chapter 1 [quoted here]

Hutton, J., 1788, Theory of the Earth: Transactions of the Royal Society of Edinburgh, vol. I, Part II, pp.209-304, plates I and II. Hutton's work is available online in several places (Univ Wisconsin, 1788 version with link to 1785 abstract, Project Gutenberg, 1795 version) and also for sale at Amazon.com.

NOTE: You can now, starting today, follow @GeologicTime on Twitter to find out, "What would 4.6 billion years of Earth history look like [when] represented by one year's worth of tweets?" I suspect that @GeologicTime will be quite busy during the latter months of the year! Read a little more about that project here.

6 comments:

Still struggling a bit with deep time, but after reading so much on evolution and geology in the last two years, I've found it easier to dive into the deep end. The truly weird thing is realizing that millions of years have become an eyeblink. I have this tendency to laugh when people talk about how old something from, say, the 50s is. You want old? Lemme show you this two billion year-old bit of rock I've got!

But I've become more comfortable with the idea that time is relative. Twenty seconds is an eternity when you're at work waiting for the clock to tick over to quitting time. Twenty million years is a mere pittance when you're talking plate tectonics, and nothing at all when set against the age of the universe. Now that you've shared your timeline trick, it should be even easier to bring these things into focus.

I find your account of how you mentally position yourself on the geological timescale fascinating. Given how spatial a lot of geology is, it's a wonderfully intuitive way to think about it.

As regards the supposed tension between Deep Time and everyday time, I think it does exist, simply because the human brain is not equipped to instinctively grasp any length of time beyond the length of a season or two. It's just that geologists, by training and experience, have learnt how to force their brains into Deep Time Mode. But it can still trip you up - I've long believed that all the long and often unfruitful Uniformitarianism/Catastrophism debate stems from a failure to grasp that from the Deep Time perspective, most 'catastrophes' are fairly commonplace.

Chris, somehow, spatial me came up with a spatial version of geologic time not dissimilar to the geologic time scale!

Yes, we've got the training and experience, and that certainly helps. And I think you're right about the Uniformitarianism v. Catastrophism debate - and possibly I hinted at this here, although I think you say it better!